I then mounted everything at their intended locations (central heating input/output pipes). For the first few hours this was working fine, and updating in domoticz as I wanted. However, a few hours later 2 out of 3 sensors stopped updating at regular intervals. One sensor is still updating nicely, while the other two only update every few hours or so (see images below).
The ESP8266 is located near the central heater, out in the open (no shielding or anything). Someone mentioned potential disturbance from the central heating pump switching on an off as a problem cause. But how would I shield for that? It still needs to receive wifi signal right?
Pink line stops regular updates after 21.30hrs:

Number 3 sensor (used as a room sensor) updates irregular:
